Devices which clamp printing plates on printing unit cylinders are known in the art. The printing unit cylinders are provided with at least one opening extending across the width of the respective cylinder. Actuating means fastened to the ends of the printing unit cylinder allow for tightening the printing plates on the outer cylindrical surface of the printing unit cylinder. The actuating means of printing unit cylinders are operable by means of an actuating unit mounted on one or both ends of the printing unit cylinder.
The state of the art, namely U.S. Pat. No. 3,016,010, discloses a tightening device for flexible printing plates. Both ends of a printing plate are clamped in a longitudinal slot of a cylinder having an actuating shaft with spring-loaded tightening elements. Both ends of the printing plate overlap each other while spring-biased collars and spring-biased engaging means are in operative engagement with the plate ends. The actuation of the shaft is achieved by means of a worm gear which is self-locking. The worm gear is provided with a tool-receiving arrangement which allows the worm gear to revolve, thereby rotating the actuating shaft. However, a tool is required for actuating the worm gear and the tightening process with the actuating shaft is rather time-consuming, since due to the reduction gear ratio, a revolution of the worm gear only results in a minimum movement of the actuating shaft.
U.S. Pat. No. 3,276,365 discloses a printing plate clamping device for a printing press. A self-arresting worm gear effects the rotation of a shaft. This shaft is formed with longitudinally extending teeth meshing with teeth formed on one side of a bar. The disadvantages of a worm gear have been outlined above.
U.S. Pat. No. 3,217,644 discloses a clamping means for mounting carrier sheets on flat or round surfaces. A cam provided with a flat is turnable by means of a manually actuatable member of a journal block. The actuatable members or arms project from their respective slots beyond the journal block, thus forming a source of danger during rotation of the cylinder. The lever mechanism only allows a turning of the cam within a narrow limited area, thus, restricting the tensioning force exerted upon the printing plate.
U.S. Pat. No. 3,359,899 shows a spring-tensioned wrap-around plate cylinder clamping arrangement. The jaws clamping the plates on the outer cylindrical surface of a cylinder are actuated by means of a tubular shaft. The rotational movement of the tubular shaft causes a translatory movement of pins engaging a jaw. The jaw, however, is spring-biased allowing the jaw to move within the slot between an engaged and a disengaged position.
Finally, U.S. Pat. No. 4,495,865 discloses a plate-clamping device for web-fed rotary printing presses. This arrangement comprises a tightening screw and a tightening lever forced against a ratchet wheel. By means of the tightening screw the ratchet mechanisms, on both sides, are loosened, thus, allowing actuating operations.